1. Field of the Invention
The present invention relates to a photoelectric conversion circuit, and more particularly, it relates to a photoelectric conversion circuit which has a function of selecting signal light from light including various disturbance light components.
2. Description of the Background Art
FIG. 41 shows the circuit structure of a conventional photoelectric conversion circuit. Referring to FIG. 41, a photodiode (PD) 1 receives light 2, and converts the same to a photoelectric conversion current (IL). An anode of the photodiode 1 is grounded through a resistor 12. A cathode of the photodiode 1 is connected with a power terminal 10, while its anode is connected with an output terminal 4 respectively. A positive voltage is applied to the power terminal 10.
When the light 2 is applied to the photodiode 1 in the photoelectric conversion circuit having the aforementioned structure, the photoelectric conversion current IL is generated in the photodiode 1. The generated photoelectric conversion current IL causes a voltage drop in the resistor 12, whereby a voltage is developed across the resistor 12 in correspondence to the intensity of the light 2. A photoelectric conversion output can be obtained by extracting this voltage at the output terminal 4. As shown in FIG. 42, the voltage developed across the resistor 12 may be temporarily amplified by an amplifier 6, to be supplied to the output terminal 4.
FIG. 43 shows another conventional photoelectric conversion circuit. An anode and a cathode of a photodiode 1 are connected to a non-inverting input terminal (+) and an inverting input terminal (-) of a differential amplifier 15 respectively. The non-inverting input terminal is grounded through a battery (E), while the inverting input terminal is connected with an output end of the differential amplifier 15 through a resistor 12. An output terminal 4 is provided on the output end of the differential amplifier 15. Also in the photoelectric conversion circuit having the above structure, a voltage corresponding to the intensity of light 2 which is applied to the photodiode 1, i.e., a photoelectric conversion output, is obtained from the output terminal 4, similarly to the circuit shown in FIG. 41.
Such a photoelectric conversion circuit is applied to a remote-control receiver for a television, a station selecting sensor for a radio, an automatic focusing apparatus or a range finder for a camera, or the like. In the remote-control receiver for a television or the station selecting sensor for a radio, the circuit is adapted to directly receive an infrared signal which is amplitude-modulated with a constant cycle when the same is remote-controlled.
In an automatic focusing apparatus or a range finder for a camera or the like, on the other hand, the circuit receives signal light of a specific frequency, being subjected to prescribed modulation, which is applied from a light source and reflected by an object. Then the circuit evaluates the distance between the object and the automatic focusing apparatus in response to the angle between the applied signal light and the reflected signal light.
In the conventional photoelectric conversion circuit having the structure shown in FIGS. 41 and 42 or FIG. 43, the photodiode 1 converts all of the received light energy to a current so that the photoelectric conversion current is further converted to a voltage by the resistor 12, whereby light components of various frequencies such as sunlight and light of artificial illumination are also photoelectrically converted. Namely, it is impossible to detect only a desired signal light component in the conventional photoelectric conversion circuit, since the circuit also receives unwanted signal components other than a signal of a specific frequency and photoelectrically converts the same.
In the conventional photoelectric conversion circuit, therefore, a malfunction is caused in the case of a remote-control receiver for a television or a station selecting sensor for a radio, while an error is caused in an automatic focusing apparatus or a range finder for a camera.